Abstract
We present an experimental thermal memory with direct optical control and readout. Information is stored in the internal temperature of the device, while laser illumination is used to read, write, and erase stored bits. Our design is based on an absorptive optical resonance in a silicon photonic crystal slab. When the slab is illuminated by a laser with a wavelength close to the resonance, the optical absorption is nonlinear with power, resulting in thermo-optic bistability. We experimentally demonstrate bistability in a fabricated device and show the reading, writing, and erasing of a single memory bit. A hybrid optothermal model shows good agreement with the experiment. Time dependent measurements show that the experimental write/erase times are less than 500 µs. We demonstrate that memory reliability is maintained over 106 cycles, with less than 3% change in the transmission values for the memory ON and OFF states. Our approach allows operation in high temperature and/or highly fluctuating temperature environment up to 100 °C or greater.
Highlights
The powerful computational capabilities provided by modern electronics fail in extreme environments, driving interest in the development of alternative computation architectures.1–4 Thermal analogues to electronic devices have been proposed as alternative route to storing and processing information, including thermal diodes,5–8 transistors,9,10 logic,11,12 and memories
We used electron-beam lithography and reactive-ion etching to pattern a silicon on insulator (SOI) wafer, with a silicon slab thickness of 340 nm, a lattice constant of 380 nm, and a hole diameter of 129 nm
We present an experimental thermal memory based on absorptive, guided-mode resonances in photonic crystal slabs
Summary
The powerful computational capabilities provided by modern electronics fail in extreme environments, driving interest in the development of alternative computation architectures. Thermal analogues to electronic devices have been proposed as alternative route to storing and processing information, including thermal diodes, transistors, logic, and memories. We deliberately increase the temperature difference between 0 and 1 states by an order of magnitude or greater relative to previous experiments.27,33 To achieve this goal, we shift our operating wavelength to the 800-1000 nm range and exploit direct absorption in silicon, while using a resonant mode to achieve strong thermo-optic nonlinearities. This type of structure is commonly known as a photonic crystal slab.. Pabs = Pin. where ωop is the operating frequency of the laser, equal to 2πc/λop, c is the speed of light in free space, γr is the decay rate of the resonance due to radiation loss, γi is the decay rate due to material absorption loss (assumed to be independent of pump power), dn/dT is the thermo-optic coefficient of silicon, and n0 is the refractive index of silicon at room temperature. We show experimentally how the bistable temperature state can be used to read, write, and erase one bit of information
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